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Planing Machine.

169

The Planing Machine, as mentioned, is not strictly
economical, because the tool cuts in one direction only, and the
back stroke is wasted. To minimise this loss, and at the same
time reverse the strcfke without changing the continuous rotation
of main shaft, ingenious motions called quick returns have been
devised.

A large-sized planing machine is given in Plate IX., as made
by Messrs. Hulse & Co. The table, stiffened with ribs, and
having T grooves on its surface to receive clamping bolts, slides
in V grooves B B, made true and level, being the copies. Thus the
work travels, and the tool is fixed. The belt pulleys c, r», E are
loose on their shaft, but c and E are technically * fast' pullies,
because they drive the table, being fixed to pinions F and G. The
strap being on pulley c, pinion F engages with wheel H ; and
pinion j on the axis of H gears with K ; L in turn with M ; lastly
pinion N moves the rack P fastened to the table. A slow cutting
advance is thus obtained. At the end of the stroke the strap is
moved from c to E, and then K is driven directly from G, the rest
being as before. Dispensing with one pair of wheels we have
effected two objects—(i) a reversal of the stroke; (2) a quicker
rotation of N, or quick return to the table. (See App. Iff., p. 918.)

When at rest the strap is on loose pulley r>, and handle Q lies
at right angles to the bed. Being connected to strap fork through
levers R, s, u, inspection shews that Q moved to the right will give
the advance, and a reverse movement the return stroke. But,
once started, these motions are automatic, thus—Let the table be
returning leftward in Fig. 171, back stop x will at end of stroke
catch lever Y, and move it to the left, shifting the strap rapidly
from E to c, the advance pulley. If the table travel to th6 right,
stop z catches Y and puts the quick return in action. These
stops may be adjusted to give various lengths of stroke.

Two vertical standards a a bolted to the bed have slides on
their front edges, and are stayed by tube b. A cross slide c lies
across them, supported by vertical screws dd, passing through
long nuts at the back. On the slide are two saddles ee, carrying
other slides//; to give a vertical movement to the tool. Screws
d d are to adjust the cross slide to any desired height, after which
it is clamped by screws gg. A handle may turn shaft h, which is